The overall goal is to establish whether a causal relationship may exist between the decreased systemic fibrinolytic activity often associated with atherosclerosis and certain types of hypertriglyceridemia (HTG) and the initiation of coronary artery thrombosis, at the endothelial cell level. Specifically, we will demonstrate that abnormal VLDL (from different types of HTG subjects) will decrease the net expression of porcine coronary artery endothelial cell (PCAEC)-mediated fibrinolytic activity and hence surface antithrombogenicity, by altering the synthesis, release and/or surface localization of fibrinolytic proteins. These studies will include the effects (short- and long-term) of VLDL (normal and HTG) on the synthesis of fibrinolytic proteins (tissue- type plasminogen activator, t-PA, urokinase-type PA, u-PA and PA inhibitor, PAI) at the level of gene transcription and/or translation of the specific mRNAs, using t-PA, u-PA and PAI activity/antigen quantitation (SDS-PAGE/125I-fibrin well assays, immunoaffinity isolation, IRMAs) and t-PA, u-PA and PAI cDNA probes (nick translation labeling, dot blot and Northern blot hybridization, autoradiography). HTG-VLDL will be classified on the basis of their ability/inability to induce rapid release (less than 2 min) of t-PA, u-PA and PAI-PA complex activity-forms - studies on the mechanism(s) of release will include identification of structural componant(s) required for release using normal and modified normal VLDL and assessment of the defective (release) componant(s) in HTG-VLDL (SDS-PAGE/125I-fibrin wells assays). The effects of HTG-VLDL on the surface receptor-mediated localization of fibrinolytic activity (antithrombogenicity ?) will involve studies on the kinetics (Eadie-Hofstee analysis) on altered PA and/or PAI-receptor binding (altered by proteolysis, adsorption, steric ?) and regulation (down/up) of PA and/or PAI receptor synthesis. These data on HTG-VLDL-mediated effects on the net expression of fibrinolytic activity in PCAECs, will provide new insights into our understanding of the early events that may contribute to the initiation of coronary artery thrombosis.